1. Field of the Invention
The present invention relates to an improved low nitrogen oxide combustion apparatus and method for use as regenerative burners and a regenerative combustion method, resulting in a low nitrogen oxide combustion and highly efficient heating system of particular value for use in high temperature industrial furnaces.
2. Description of Related Art
The conventional regenerative burner is comprised of a pair of burner means consisting of a separate regenerating section 2 and fuel supply section 13, attached to the main furnace, as shown in Prior Art FIG. 6. In this case, the air is introduced from the air inlet or air introducing section 9, as shown by the arrows in the drawing, to one of the burner means 11a where it is preheated in the regenerating section 2. Then, preheated air is mixed with the fuel injected from the fuel supply section 13a, and the air-fuel mixture is ignited and the flame is subsequently injected into the furnace 4, where it continues to burn. The exhaust gas from the furnace 4 is further used for heat exchange, i.e. for heat regeneration, in the regenerating section of the next burner means 11b, and subsequently exits through the exhaust section 10. These burner means 11 are alternately used for burning and exhausting at very short intervals of tens of seconds to several minutes.
This combustion method, i.e., regenerative combustion method, can achieve a higher waste heat recovery rate resulting in greater fuel saving and it is also important when considering environmental protection concerns as this method also results in decreased CO.sub.2 emissions.
Although the conventional regenerative combustion method is excellent as a means of increasing the rate of waste heat recovery, it has a very large disadvantage in that the temperature of the preheated combustion air is so high that the flame temperature is raised, which results in remarkably increased nitrogen oxide (NOx) emission.
Even if any conventionally known NOx decreasing techniques are applied to the regenerative combustion method, such as the staged combustion method, the exhaust gas recirculation method, or the water spray method, the NOx emission can be decreased at the most, by only 50 to 60%, from 500-1200 ppm (O.sub.2 11%) to 200-500 ppm (O.sub.2 11%). This reduction does not meet the regulatory level of 180 ppm (O.sub.2 11%) required by the Air Pollution Control Law of Japan.
The object of the present invention is to provide a combustion apparatus and combustion method which can achieve low NOx emissions even when used as a regenerative burner or as part of a regenerative combustion method, sufficient to heat combustion air to high temperatures, and which can achieve stable combustion, even with wide ranging furnace temperature.